1. Field of the Invention
The present invention relates to a method for separating a styrene polymer useful in the field of electrophotographic toner by continuously treating a reaction mixture containing the styrene polymer prepared by the homopolymerization of styrene monomer or its copolymerization with other vinyl monomer to separate and remove volatile ingredients such as unreacted monomer, polymerization solvent and decomposition product of polymerization initiator by use of a specific separation equipment of the volatile ingredients.
2. Description of the Prior Art
Methods for separating the bulk- or solution-polymerized styrene polymer from the reaction mixture have been disclosed in Japanese Patent Publication Nos. 31678/1970, 29797/1973 etc. The styrene polymer described in these publications has a relatively high molecular weight in order to use, for example, for molding application. These methods have a disadvantage and not suitable for treating the reaction mixture containing the styrene polymer of this invention.
For example, Japanese Patent Publication No. 29797/1973 discloses a method for using a vertical multitubular heat-exchanger. In the case, however, of applying the heat-exchanger for the reaction mixture of styrene poller in this invention, flow rate of the reaction mixture into the heating zone is remarkably increased. This is because the low molecular weight polymer always existing in the aforesaid reaction mixture is formed by the reduced pressure in the heat exchanger. Therefore the flow line of reaction mixture still maintains its original direction after flowing into the heating zone, and the distribution of flow amount to each tube tends to be uneven in the heating zone. This phenomenon results in variation of flow amount, flow amount distribution and residence time in the heating zone. Consequently the efficiency for removing the volatile ingredients is found to have a remarkable fluctuation and the quality of product is greatly dareaged. It is of course possible to homogenize the flow amount distribution to some extent by fitting a dispersion plate at the inlet of heating zone. It, however, is still unsatisfactory so long as the vertical multitubular heat-exchanger is used.